This application claims priority of Taiwanese Application No. 091210644, filed on Jul. 12, 2002.
1. Field of the Invention
The present invention relates to a coupling device to be coupled to a rotary drive unit for enabling transmission of rotation from the drive unit, more particularly to a coupling device with an enhanced transmission efficiency and a longer service life.
2. Description of the Related Art
A coupling device is a device that couples a work shaft to a rotary-drive unit so as to enable the work shaft to rotate with the drive unit. FIG. 1 illustrates a conventional coupling device which includes a bearing seat 100, a transmission shaft 200, a clutch wheel 30, first and second coupling plates 50, 40, and a work shaft 60. The seat 100 is stationary, and includes a tubular part, that defines an axial hole 101. Two bearing rings 102 are mounted in the axial hole 101. The transmission shaft 200 has a rear end extending through the axial hole 101 and the bearing rings 102 and to be coupled to a rotary drive unit (not shown), and a front end provided with a mounting block 201 which is formed with a semi-circular cavity 203 that opens upwardly and forwardly. The mounting block 201 has a pivot hole 205 formed through a lower end thereof and extending transverse to an axis of the transmission shaft 200. The clutch wheel 30 is formed with a central hole 301 which has a shape generally corresponding to that of the mounting block 201. The mounting block 201 extends into the central hole 301 so as to be coupled co-rotatably with the clutch wheel 30. The clutch wheel 30 has a pivot hole 302 formed therethrough and aligned with the pivot hole 205 in the mounting block 201. A pivot axle 303 extends through the pivot holes 302, 205 in the clutch wheel 30 and the mounting block 201 for mounting the clutch wheel 30 pivotally on the mounting block 201. The first coupling plate 50 is fan-shaped, and is fastened to a front side surface of the clutch wheel 30 adjacent to the central hole 301. The second coupling plate 40 is disposed on a front side of the clutch wheel 30, and is fastened to a front end wall of the mounting block 201. When the clutch wheel 30 is in a first position in which the clutch wheel 30 is perpendicular to an axis of the transmission shaft 200, as shown in FIG. 2, the first and second coupling plates 50, 40 cooperatively form a circular disk, and cooperatively confine a polygonal coupling hole 401 registered with the central hole 301 in the clutch wheel 30 and the cavity 203 in the mounting block 201. The work shaft 60 has a coupling end portion 601 with a polygonal cross-section corresponding to that of the coupling hole 401.
In use, the clutch wheel 30 together with the first coupling plate 50 mounted thereon are moved pivotally relative to the mounting block 201 to a second position shown in FIG. 3, in which the clutch wheel 30 extends along another plane that is inclined relative to the axis of the transmission shaft 200. In this position, the first coupling plate 50 is spaced apart from the second coupling plate 40 to permit access to the coupling hole 401, and a top opening of the cavity 203 in the mounting block 201 is exposed at this time. The coupling end portion 601 of the work shaft 60 can thus be extended into the coupling hole 401 and into the cavity 203 from above. The clutch wheel 30 is then moved pivotally back to the first position shown in FIG. 2 such that the coupling end portion 601 is received in the coupling hole 401 and is coupled co-rotatably with the first and second coupling plates 50, 40, the clutch wheel 30 and the mounting block 201. The work shaft 60 is thus coupled to the transmission shaft 200 so as to permit transmission of rotation from the rotary drive unit (not shown) to the work shaft 60.
It is noted that connection between the work shaft 60 and the transmission shaft 200 is achieved by the coupling between the polygonal coupling end portion 601 of the work shaft 60 and the polygonal coupling hole 401 confined by the first and second coupling plates 50, 40. High precision is thus required when forming the polygonal coupling end portion 601 of the work shaft 60 and the first and second coupling plates 50, 40. This unavoidably increases the manufacturing cost. Moreover, slight deviations in the precision of the size and shape of the polygonal coupling end portion 601 and the polygonal coupling hole 401 can cause the polygonal coupling end portion 601 to collide with the first and second coupling plates 50, 40 during rotation. This results in noise and in wear and tear of these components to thereby reduce the service life of the conventional coupling device.
Therefore, the main object of the present invention is to provide a coupling device with enhanced transmission efficiency and a longer service life.
Accordingly, the coupling device of the present invention includes a transmission member and a work shaft. The transmission member includes a cylindrical rod with an axis, a rear end adapted to be coupled to a rotary drive unit so as to be rotated by the drive unit, a front end, and a circumferential outer surface extending between the front and rear ends. The transmission member further includes a curved coupling flange which has a cross-section in the form of a circular sector and which extends circumferentially and co-axially along the outer surface of the cylindrical rod. The coupling flange is fixed to the outer surface of the cylindrical rod and projects forwardly relative to the front end of the cylindrical rod. The coupling flange has a concave face confronting the axis of the cylindrical rod and formed with a plurality of engaging protrusions, and a convex face opposite to the concave face. The work shaft includes a main body which extends along the axis of the cylindrical rod of the transmission member and which has a spherical end, and a tubular sleeve sleeved on the spherical end and co-rotatable with the spherical end. The tubular sleeve cooperates with the spherical end to form a coupling end portion of the work shaft. The tubular sleeve is formed with a plurality of engaging grooves which are angularly displaced from one another with respect to the axis of the cylindrical rod of the transmission member. The coupling end portion is disposed on the concave face of the coupling flange so as to enable engagement between the engaging grooves and the engaging protrusions in order to permit transmission of rotation of the transmission member to the work shaft.